A coupling element for connecting a helix-shaped eccentric screw pump rotor to a drive shaft, with a drive shaft receiving portion and a rotor connecting portion arranged at an opposite end of the coupling element from the drive shaft receiving portion, the rotor connecting portion is constituted as a hollow cylinder for receiving a rotor end of the screw pump rotor, wherein the hollow cylinder has at least two inner circumferential surfaces which are complementary to the rotor and have a radius which is fixed with respect to the cross-sectional center of the hollow cylinder.